This invention relates to the preparation of demand-type broad-spectrum resin-polyiodide water disinfectants. Triiodide-quaternary ammonium resin disinfectants have heretofore received primary consideration, since when properly prepared, the iodine is tenaciously bound to the active sites of the resin and is released almost entirely on a demand-action basis. See Lambert and Fina U.S. Pat. Nos. 3,817,860 and 3,923,665. Also, see Fina, L. R. and Lambert, J. L. (1975), "A Broad-Spectrum Water Disinfectant that Releases Germicide on Demand," Second World Congress, International Water Resources Association, New Delhi, India, December 1975, Volume II, pp. 53-59.
Prior to the present invention, the preferred procedure for preparing the triiodide resins has been to form the triiodide ion in aqueous solution by dissolving iodine in a water solution of sodium or potassium iodide. The resulting solution containing the triodide ion is then applied to the resin, the triiodide ion exchanging with the anion of the resin as supplied by the manufacturer (usually chloride or sulfate). With this procedure, it has been found difficult to prepare resins containing only triiodide and in which all of the active sites of the resin have been converted to triiodide. After forming the resin, it has been necessary to wash it with water and/or with aqueous solutions of potassium iodide. There has been a need for a process where the desired form of the resin can be prepared directly on an exact stoichiometric basis.
It has been suggested that the resin could first be converted to the iodide, and then reacted with elemental iodine to form the triiodide. However, prior to the present invention, this procedure was not believed to be desirable for commercial purposes. As stated in U.S. Pat. No. 3,923,665 (col. 3, lines 62-69):
"In another procedure, the resin is first converted to the iodide (I.sup.31 ) form by contacting it with a solution of potassium or sodium iodide, or other iodide salt, and a stirred aqueous slurry of the converted resin is contracted with elemental iodine. (I.sub.2) to react with the absorbed I.sup.- to form bound I.sub.3.sup.-. This procedure is less desirable, since it is more difficult to assure precise saturation of the column with triiodide."
In applying elemental iodine to resin beads, the problem of iodine encrustation has been encountered. As the iodine is applied in aqueous solution, it tends to form a crust on the outside of the beads, comprising a deposit of I.sub.2. Further, it has been difficult to obtain homogeneous products in which the iodine has been uniformly distributed throughout the resin beads being treated.